Bubble shape and rising velocity in viscous liquids at high temperature and pressure

Industrial bubble column reactors use to operate at high pressure and temperature. However, few experimental investigations have been performed under such severe conditions. In this work the effects of high pressure (0.1-6 MPa) and high temperature (293-473 K) on the bubble shape and rising velocity in silicone oil and paraffin are experimentally investigated. The experiments are carried out in a stainless steel bubble column of 50 mm I.D with three pairs of high strength quartz windows. The bubble flow is visualized and recorded through high speed camera. New correlations for bubble aspect ratio E are proposed by use of the experimental data. The correlations are divided into three parts in terms of Weber number and Morton number. For We > 12, bubble aspect ratio is independent of Weber number, and is only related to Morton number. For We < 12 and Morton number larger than 3, bubble aspect ratio is only related to Reynolds number. For Morton number lower than 3, the aspect ratio could be expressed in terms of the Eotvos number and Reynolds number. Bubble rise velocity decreases with increasing pressure and decreasing temperature, which could be attributed to the variations of liquid viscosity, gas density, and bubble surface property. A modified correlation of Fan and Tsuchiya is recommended for bubble rise velocity valid at high temperature, high pressure and viscous liquids.